Function expansion unit capable of supplying power to computer

ABSTRACT

A system includes a computer main body, and an expansion unit detachably connected to the computer main body, for supplying a power to the computer main body and expanding a function of the computer. A power in the expansion unit is consumed in the expansion unit prior to power supply to the computer main body so as to stably supply a power to circuit components of the expansion unit. The expansion unit includes an expansion connector to which at least one expansion board is arbitrarily detachably connected, a power supply for supplying the power to the circuit components including the expansion circuit boards and to the computer main body, and a switch for detecting a power supplied from the power supply to the circuit components and stopping power supply to the computer main body by the power supply when the power exceeds a predetermined value.

This is a division of application Ser. No. 07/777,190, filed on Oct. 16,1991, U.S. Pat. No. 5,301,334.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a function expansion unit preferablyused in a portable computer and, more particularly, to a functionexpansion unit having a function of supplying a power to a computer.

2. Description of the Related Art

In a personal computer field, a laptop or book-type portable personalcomputer having a light weight and a small size has prevailed, and hasbeen frequently used as a low-end machine. The laptop personal computercannot support many functions as standard functions to maintain goodportability of the computer. A high-grade function is generallypresented as an optional function. More specifically, a high-gradefunction is presented as a function expansion card (to be referred to asonly an expansion card or a circuit board hereinafter), and theexpansion card is inserted into the vacant slot of a function expansionunit (to be referred to as only an expansion unit hereinafter) to beconnected to the personal computer, thereby obtaining the high-gradefunction.

An expansion unit capable of supplying a power to a personal computer isdisclosed in, for example, U.S. patent application Ser. No. 578,533 andEuropean patent application 90117214.8. The contents of the U.S. andEuropean patent applications are incorporated as a reference in thisspecification. Personal computers driven by a battery are generallyused, and power supply from the expansion unit to the personal computeris performed in a DC manner.

However, when an expansion circuit board itself has high powerconsumption, or when a plurality of expansion circuit boards arearranged in a personal computer, total power consumption may exceed apower which can be supplied by an expansion unit. This may cause theerroneous operation or breakdown of the personal computer.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovecircumstances, and has as its object to provide an expansion unit cableof supplying a power to a computer and improving function expansibilitysuch that power supply to the computer is stopped depending on powerconsumption of the expansion unit so as to preferentially consume apower in the expansion unit.

Another object of the present invention is to provide an expansion unitcapable of supplying a power to a computer and increasing the operationreliability of the expansion unit by ON/OFF-operating power supply tothe computer in accordance with power consumption of an expansion boardto be mounted in the expansion unit.

In order to achieve the above objects, according to the presentinvention, there is provided an expansion unit (1), detachably connectedto the computer main body (2), for supplying a power to the computermain body (2) and expanding a function of the computer,

the expansion unit (1) including:

expansion connector means (295) to which at least one expansion board(13) is arbitrarily detachably connected;

power supply means (15) for supplying the power to circuit componentsincluding the expansion circuit boards (13) and to the computer mainbody (2); and

switching means (11, 12) for detecting the power supplied from the powersupply means (15) to the circuit components and stopping power supply tothe computer main body (2) by the power supply means (15) when the powerexceeds a predetermined value.

With the above arrangement, when power consumption of the expansion unitis high, power supply to the computer main body is stopped. Therefore,the power supply means can supply a power to circuits of the expansionunit with a certain margin, and a normal operation of the expansion unitcan be assured.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram showing an arrangement of an expansion unitaccording to the first embodiment of the present invention;

FIG. 2 is a perspective view showing a state wherein an expansion unitand a personal computer according to the first embodiment of the presentinvention are connected to each other;

FIG. 3 is a perspective view showing a personal computer according tothe second embodiment of the present invention;

FIG. 4 is a perspective view showing a connecting method of an expansionunit and a personal computer according to the second embodiment of thepresent invention;

FIG. 5 is a perspective view showing a state wherein the expansion unitand the personal computer according to the second embodiment of thepresent invention are connected to each other;

FIG. 6A is a block diagram showing a circuit arrangement of the personalcomputer according to the second embodiment of the present invention;

FIG. 6B is a block diagram showing a circuit arrangement of theexpansion unit according to the second embodiment of the presentinvention;

FIG. 7 is a circuit diagram showing an arrangement of a power supplycircuit and a switch controller shown in FIG. 6B; and

FIGS. 8, 9 and 10 are circuit diagrams showing other switch controllers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

In FIGS. 1 and 2, reference numeral 1 denotes an expansion unit, andreference numeral 2 denotes a personal computer. Reference numerals 11to 15 denote elements or components arranged in the expansion unit 1.The reference numeral 11 denotes a current detection circuit, and thecurrent detection circuit 11 detects power consumption of expansioncards or boards 13, i.e., the value of a current flowing throughcircuits of the expansion boards 13. The reference numeral 12 denotes aswitching circuit turned on/off in accordance with the detection resultobtained by the current detection circuit 11. The three expansion boards13 are connected to the expansion unit 2. The reference numeral 14denotes a display circuit for informing a user of the ON or OFF state ofthe switching circuit 12. An LED, a buzzer, or the like is used as thedisplay circuit. This information may be performed by displaying amessage on a display connected to the personal computer 2. The referencenumeral 15 denotes a power supply circuit arranged in the expansion unit1, and the power supply circuit 15 supplies a charge power and anoperation power to not only the expansion boards 13 inserted into theexpansion unit 1 and circuit parts but to the personal computer 2.

FIG. 2 shows a state wherein the personal computer 2 is connected to theexpansion unit 1. The expansion boards 13 are inserted into theexpansion unit 1 from a direction of an arrow A in FIG. 2.

The operation of the embodiment will be described below.

The power supply circuit 15 supplies a power to the personal computer 2and the expansion boards 13 connected to the expansion unit 1. The powerdetection circuit 11 is arranged between the power supply circuit 15 andthe expansion boards 13. The current detection circuit 11 detects anovercurrent state of power consumption. The switch 12 is arrangedbetween the power supply circuit 15 and the external power supply inputportion of the personal computer 2. The switch 12 is turned off when thecurrent detection circuit 11 detects a predetermined value or more, andthe switch 12 is turned on when the current detection circuit 11 detectsthe predetermined value or less.

The ON or OFF state of the switch 12 is informed to a user by thedisplay means 14. The user makes a countermeasure by this informationsuch that an AC adapter is connected to a personal computer driven by abattery before the battery is dead.

With the above description, the present invention is described using acase wherein a power is supplied from an expansion unit to a personalcomputer. However, the present invention is not limited to the abovedescription, and the present invention can be applied to any machine inwhich a power is supplied from one power supply to two or more devices.

According to this embodiment, when an expansion board itself has highpower consumption or when a plurality of expansion boards are used, auser can use an expansion unit regardless of the magnitude of the powerconsumption. Even if power supply to a personal computer is interrupted,a user can made some countermeasure by a function of informing thisinterruption. For example, since a laptop personal computer connected toan expansion unit is generally driven by a battery, temporaryinterruption of power supply causes no problem. Therefore, the followingcountermeasure is made. That is, an AC adapter (external power supply)is connected to the personal computer while the personal computer isdriven by the battery.

Second Embodiment

The second embodiment of the present invention will be described indetail with reference to FIGS. 3 to 7.

FIG. 4 shows an expansion unit according to the second embodiment of thepresent invention and a personal computer 21 serving as a compactelectronic equipment in which the expansion unit is mounted. A computer1 is called a note-type or book-type personal computer. The computer 21includes a battery pack 22 detachably connected to rear portion of amain body 28 and a flat panel display device 23. The display device 23can be pivoted about a pivotal support portion 25 to stand upright.

The computer 21 includes a keyboard 27 arranged at the front portion ofthe main body 28. A connector 26 is arranged on the rear surface of themain body 28. The connector 26 has a large number of parallel terminals.A power supply socket 29 commonly used for a feeder plug 35 of anexpansion unit 31 (to be described later) and a feeder plug of an ACadapter (external DC power supply) 43 is arranged on a side surface ofthe computer 21. These feeder plugs are inserted and connected to thepower supply socket 29.

The expansion unit 31 will be described below.

The expansion unit 31 includes a casing 32. A power supply code 34, adistal end of which has a feeder plug 35 inserted and connected to thepower supply socket 29 of the computer 21, is drawn from one sidesurface of the casing 32. The front portion of the casing 32 is formedas a support table portion 33 on which the rear portion of the computer21 is mounted. A support plate 36 which can slide forward from thecasing to the front portion of the casing along a direction of an arrowD in FIG. 4 is arranged on the bottom of the casing 32.

A connector unit 38 is arranged on the casing 32 at a position oppositeto the connector 26 of the computer 21 mounted on the support tableportion 33.

The connector unit 38 includes a handle 39 and a slider 40 moved to beinterlocked with the handle 39 upon its pivotal movement. The slider 40supports an insertion connector 41 having a guide pin and a plurality ofterminals. The connector 41 is formed to be inserted and connected tothe connector 26 of the computer 21. The connector 41 is arranged in afloating state by a spring with respect to the slider 40.

A procedure of connecting the computer 21 to the expansion unit 31 willbe described below.

First, the support plate 36 is drawn forward from the casing 32. Therear portion of the computer 21 is mounted on the support table portion33 of the casing 32, and the front portion of the computer 21 is mountedon the support plate 36.

In this state, when the handle 39 is pivoted moved forward, the slider40 is pushed out forward accordingly, and the connector 41 is pushed outtogether with the slider 40. Immediately before the connector 41 isbrought into contact with the connector 26, the distal ends of the guidepins are inserted into through holes of the connector 26, and theconnector 41 is accurately positioned with respect to the connector 26.

When the slider 40 is further moved forward, the connector 41 is fittedin the connector 26. As a result, a signal can be transmitted/receivedbetween the computer 21 and the expansion unit 31.

Circuit arrangements of the expansion unit 31 and the personal computer21 will be described below with reference to FIGS. 6A to 7.

In the computer main body 21, the respective components are directly orindirectly connected to each other through a system bus 170 (a controlbus 170a, a date bus 170b, and an address bus 170c). The system bus 170is connected to the connector 26.

The CPU 111 controls the overall operation of this system. A BIOS (basisinput/output system)-ROM (read only memory) 112 stores programs and thelike for controlling I/O (input/output) devices. When the expansion unit31 is connected to this computer main body 21, the I/O interface of theexpansion unit 31 is used in place of the I/O interface of the computermain body 21. A system RAM (random access memory) 113 stores programsand data to be processed. A backup RAM 114 stores data and the like whenresume processing is performed. While the system power supply is turnedoff, power is supplied to the backup RAM 114 in order to back up storeddata. A bus driver (BUS-DRV) 115 is arranged between a CPU bus 172 (acontrol bus 172a, a data bus 172b, and an address bus 172c) and thesystem bus 170 so as to perform data transmission/receptiontherebetween. A memory controller (M-CNT) 116 performs access controlwith respect to the ROM 112 and the RAMs 113 and 114 under the controlof the CPU 111.

A power supply (PS) 120 applies DC operating voltage (+12 V, -12 V, -9V, +5 V, and -5 V) to the respective components by using a DC voltage(+15 v) from a AC adapter 43 (FIG. 6B) or the expansion unit 31connecter to a power supply connecter 29. In addition, a voltage (+5 V)from the power supply 120 is applied as an operation check signal to theexpansion unit 31 through the connector 26, 41.

That is, if the expansion unit 31 is not connected to the computer mainbody 21, the power supply connector 29 is connected to the AC adapter43, and a DC output voltage (+15 V) from the AC adapter 43 is applied tothe power supply 120. If the expansion unit 31 is connected, the powersupply connector 29 is connected to a power supply connector 35 of theexpansion unit 31, and DC power (+15 V) is supplied from the powersupply 252 to the power supply 120. A switch 121 is used to turn on andoff the power supply 120.

A secondary Battery (BAT) 122 can be detached and serves to supply powerto the power supply 120. Therefore, when no power is supplied from anexternal circuit, the power supply 120 can supply an operating power tothe internal components for a certain period. In addition, when a poweris supplied from an external circuit, the power supply 120 charges thesecondary battery 122.

A printer interface 131 is arranged between the system bus 170 and aprinter connector 180a so as to transmit/receive data to/from a devicesuch as a printer connected to the printer connector 180a. A firstRS-232C interface 132 is arranged between the system bus 170 and RS-232Cconnector 180b so as to transmit/receive data and the like to/from adevice connected to the RS-232C connector 180b. A second RS-232Cinterface 133 is arranged between the system bus 170 and the RS-232Cconnector 180c so as to transmit/receive data and the like to/from adevice connected to the RS-323C connector 180c.

In addition, the computer main body 21 includes a programmable intervaltimer (PIT) 133 which can be set by a program, a keyboard controller(KBC) 134, a scan controller (SC) 135, a keyboard (KBC) 136, a hard diskcontroller (HDC) 137, a hard disk drive (HDD) 138, a floppy diskcontroller (FDC) 139, a floppy disk drive (FDD) 140, a displaycontroller (DISP-CNT) 141, a video RAM (VRAM) 142 capable of data backupduring a power-OFF period, and a display unit (DISP) 143 constituted bya plasma display or the like.

In the expansion unit 31 shown in FIG. 6B, the respective components aredirectly or indirectly connected to each other through a system bus 290(a control bus 290a, a data bus 290b, and an address bus 290c). Notethat the system bus 290 is connected to the system bus 170 of thecomputer main body 21.

The system bus 290 is connected to an expansion bus connector 295, andan expansion board 204 is selectively connected to the expansion busconnector 295 as needed. The respective components of the expansion unit31 will be described below.

Upon reception of an operation check signal (+5 V) from the power supply120 of the computer main body 21, a voltage detector (DET) 251 outputs apower supply enable signal to the power supply (PS) 252.

The power supply 252 comprises an AC/DC converter 252a, a power supplycontroller 252b, and a constant voltage circuit 252c, as shown in FIG.7.

The AC/DC converter 252a rectifies/smoothes a commercial AC voltage fromthe power supply adapter and generates a DC voltage (+15 V, +12 V, -12V, +5 V, and -5 V).

The constant voltage circuit 252c supplies DC operating voltages (+12 V,-12 V, +5 V, and -5 V) from the AC/DC converter 252a to the respectivecomponents of the expansion unit 31, and supplies a DC voltage (+15 V)to the power supply 120 of the computer main body 21.

The power supply controller 252b controls supply of DC voltages from theconstant voltage circuit 252c. More specifically, no DC operatingvoltages (+12 V, -12 V, +5 V, and -5 V) are supplied to the respectivecomponents of the expansion unit 31 until a power supply enable signalfrom the voltage detector (DET) 251 is received.

A switch 253 shown in FIG. 6B is used to turn on and off the powersupply 252 of the expansion unit 31.

An ID register (ID-REG) 254 is connected to the system bus 290 of theexpansion unit 31 so as to store unit ID data inherent in the expansionunit 31. A port address assigned to the I/O port of each I/O interfaceof the expansion unit 31 can be recognized by referring to this unit IDdata.

An address decoder (DEC) 255 performs address detection with respect tothe ID register 254.

A printer interface 261 is arranged between the system bus 290 and aprinter connector 285a so as to transmit/receive data and the liketo/from a device such as a printer connected to the printer connector285a.

A first RS-232C interface 262 is arranged between the system bus 290 andan RS-232C connector 285b so as to transmit/receive data and the liketo/from a device connected to the RS-232C connector 285b. In addition, asecond RS-232C interface 263 is arranged between the system bus 290 andan RS-232C connector 285c so as to transmit/receive data and the liketo/from a device connected to the RS-232C connector 285c.

As a characteristic feature of this embodiment, an arrangement forstopping power supply from the expansion unit 31 to the computer mainbody 21 will be described below. As shown in FIG. 6B, voltages (+5 V,+12 V, -5 V, and -12 V) are supplied from the power supply 252 to theexpansion board 204 as operating voltages. The current values of thevoltages are measured by a switch control circuit 300. The switchcontrol circuit 300 supplies a control signal to a switch SW to open theswitch SW when the power consumption of the expansion unit 31 exceeds apredetermined value, and stops power supply from the expansion unit 31to the computer main body 21. The control signal output from the switchcontrol circuit 300 is also supplied to a loudspeaker driver 321. Aloudspeaker 313 is driven by the loudspeaker driver 321 in response tothe control signal so as to generate an alarm.

The arrangement of the switch control circuit 300 will be described indetail with reference to FIG. 7. The current values of voltages (+5 V,+12 V, -5 V, and -12 V) output from the constant voltage circuit 252care measured by ammeters 301 to 304. The measured current values aresupplied to the positive input terminals of corresponding comparators305 to 309. Signals having predetermined reference current values Ir1 toIr4 are supplied to the negative input terminals of the comparators 305to 309, respectively. When the measured current values exceed thepredetermined reference values Ir1 to Ir4, respectively, the outputsfrom the corresponding comparators 305 to 309 go to high level. Thereference current values Ir1 to It4 are independently and appropriatelydetermined in accordance with the capacity of the power supply 252.

The measurement values of the ammeters 301 to 304 are supplied to anarithmetic circuit 310. The arithmetic circuit 310 calculates powerconsumption of each voltage from the measurement values of the ammeters301 to 304 and the current values corresponding to the measurementvalues, and compares a sum of the obtained power consumption of thevoltages with a predetermined set value. The arithmetic circuit 310outputs a high-level signal when the sum of power consumption is largerthan the set value.

Outputs from the comparators 305 to 309 and the arithmetic circuit 310are supplied to an OR circuit 311. An output from the OR circuit 311 issupplied to a control terminal of the switch Sw, and the switch SW isopened when the output from the OR circuit 311 goes to high level. Forthis reason, a power of +15 V supplied from the power supply 252 to thepower supply 120 is forcibly interrupted. However, the power supply 120can be operated by a power supplied from the secondary battery 122. Whena user connects the AC adapter 43 to the power supply connector 29 inresponse to an alarm generated from a loudspeaker 313, the computer mainbody 21 can be operated by an external power supply.

The operation of this system after an expansion unit 31 is connected tothe computer main body 21 will be described below.

After the connection between the connector 26 and the connector 45 andthe connection between the feeder plug 35 and the connector 29 arecompleted, when the switch 253 of the expansion unit 31 is turned onwhile the switch 21 is set in an OFF state, the power supply 252supplies a voltage (+15 V) to the computer main body 21 through theswitch SW, a cable 34, the feeder plug 35, and the connector 29. In thiscase, operating voltages (+12 V, -12 V, +5 V, and -5 V) are not suppliedto the respective components.

when the switch 121 is turned on, the power supply 120 of the computermain body 21 supplies operating voltages (+12 V, -12 V, -9 V, +5 V, and-5 V) to the respective components of the computer main body 21 on thebasis of the voltage (+15 V) from the power supply 120. A voltage (+5 V)from the power supply 120 is supplied to the expansion unit 31 throughthe connectors 26 and 45.

When a voltage (+5 V) is detected in the voltage detector 251 of theexpansion unit 31, an operation confirming signal is supplied to thepower supply 252. In the power supply controller 252b of the powersupply 252, it is determined by this operation confirming signal thatthe computer main body 21 is set in an operation enable state. Anoperating voltage is supplied to the respective components of theexpansion unit 31 and the expansion board 204.

According to the above operation, power supply control at a systemstarting operation is completed, and the operations of the respectivecomponents are started.

In an operating state of the system, for example, it is assumed thatconsumption of a power having a voltage of +5 V is sharply increased dueto high power consumption of one of the expansion boards 204. In thiscase, an output from the comparator 301 goes to high level, and anoutput from OR gate 311 goes to high level, thereby opening the switchSW. For this reason, the power of +15 V supplied to the computer mainbody 21 is interrupted. Therefore, the constant voltage circuit 252c cansupply a power of +15 V with a relatively large margin. In addition,since the loudspeaker 313 generates an alarm, a user can make acountermeasure, e.g., an AC adapter 43 is connected to the power supplyterminal 29.

In the operating state of the system, for example, it is assumed thattotal power consumption is increased. In this case, an output from thearithmetic circuit 310 goes to high level, and an output from the ORgate 311 goes to high level, thereby opening the switch SW. For thisreason, a power of +15 V supplied to the computer main body 21 isinterrupted, and the loudspeaker 313 generates an alarm.

As described above, according to the present invention, when aconsumption amount of a power having a specific voltage value isincreased, or when total power consumption is increased, power supply tothe computer main body 21 is stopped. Therefore, the power supply to thecomponents and the expansion board 24 in the expansion unit 31 can bestably performed with a relatively large margin.

The present invention is not limited to the above embodiment. Forexample, in the above embodiment, the currents of the outputs (+5 V, +12V, -5 V, and -12 V) from the constant voltage circuit 252c are measured.However, only the outputs having positive voltages generally have largecurrent values. Therefore, for example, the control circuit 300 may beconstituted such that the ammeters 302 and 304, the comparators 306 and308, and the arithmetic circuit 310 may be omitted except for theammeters 301 and 303 and the comparators 305 and 307, as shown in FIG.8.

As shown in FIG. 9, the current value of the power of +15 V supplied tothe computer main body 21 is measured by an ammeter 321, and theresultant value may be supplied to the comparator 322 and the arithmeticcircuit 310. In this case, when an output power from the power supply252 exceeds the capacity of the power supply 252, power supply to thecomputer main body 21 can be stopped.

As shown in FIG. 10, the switch SW may be ON/OFF-controlled so as tocheck only the power consumption of the expansion board 204 which is themost decisive cause of a change in power consumption of the expansionunit 31.

For example, a wattmeter may be arranged in place of an ammeter, and apower of each voltage may be measured. The switch SW may beON/OFF-controlled so as to compare the powers with a reference value.

The switch SW may be constituted by, e.g., a relay switch, a transistorswitch, a MOSFET, or the like.

According to this embodiment, in an expansion unit for supplying a powerto a computer main body, when power consumption of the expansion unit(including an expansion board) is increased, power supply to thecomputer main body is stopped. Therefore, powers can be stably suppliedto the expansion board and components in the expansion unit.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may be withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

What is claimed is:
 1. An electronic equipment to which an externalequipment is detachably connected through a power connector, saidelectronic equipment including internal circuit components,comprising:power supply means, coupled to the power connector and theinternal circuit components, for supplying an external power to saidexternal equipment through the power connector and supplying an internalpower to said internal circuit components; and switching means, coupledto said power supply means, for detecting whether an amount of theinternal power supplied from said power supply means exceeds apredetermined value and preventing the external power from beingsupplied to said external equipment when the amount of the internalpower exceeds said predetermined value, thereby enabling said powersupply means to supply the internal power for a normal operation of saidinternal circuit components.
 2. An equipment according to claim 1,further comprising means, coupled to said switching means, for informinga user of said external equipment that the external power is notsupplied to said external equipment while said switching means preventsthe external power from being supplied to said external equipment.
 3. Anequipment according to claim 1, wherein said switching meansincludes:current value measuring means, coupled to said power supplymeans, for measuring a current value of the external power; comparingmeans for receiving a measurement value from said current valuemeasuring means, comparing the measurement value with a predeterminedreference value, and outputting an indicating signal indicating whetherthe measurement value is greater than the predetermined reference value;and a switch which is arranged in series between said power supply meansand said power connector, receives the indicating signal from saidcomparing means and opens when the indicating signal indicates that themeasurement value is greater than the predetermined reference value. 4.An equipment according to claim 3, wherein said power supply meansoutputs a plurality of currents having different voltage values, saidcurrent value measuring means independently measures values of theplurality of currents, said comparing means compares measurement valuesobtained by independently measuring the plurality of currents with apredetermined reference value for each current and instructs said switchto be opened when a value of at least one current is larger than thepredetermined reference value.
 5. An equipment according to claim 1,wherein said external equipment comprises a portable computer and saidelectronic equipment comprises an expansion unit for expanding afunction of said portable computer.
 6. An electronic equipment to whichan external equipment is detachably connected through a power connector,comprising:an internal circuit component variably consuming power; powersupply means, coupled to the power connector and said internal circuitcomponent, for supplying an external power to said external equipmentthrough the power connector and supplying an internal power to saidinternal circuit component; means, coupled to said power supply means,for detecting that an amount of the internal power supplied from saidpower supply means exceeds a predetermined value; and means, coupled tosaid detecting means, for preventing the external power from beingsupplied to said external equipment while said detecting means detectsthat the amount exceeds the predetermined value, thereby enabling saidpower supply means to supply the internal power for a normal operationof said internal circuit component.
 7. An equipment according to claim6, further comprising means, coupled to said preventing means, forinforming a user of said external equipment that the external power isnot supplied to said external equipment while said preventing meansprevents the external power from being supplied to said externalequipment.
 8. An equipment according to claim 6, wherein said detectingmeans includes:current value measuring means, coupled to said powersupply means, for measuring a current value of the external power; andcomparing means for receiving a measurement value from said currentvalue measuring means and comparing the measurement value with apredetermined reference value.
 9. An equipment according to claim 6,wherein said external equipment comprises a portable computer and saidelectronic equipment comprises an expansion unit for expanding afunction of said portable computer.
 10. An electronic equipment to whichan external equipment is detachably connected through a power connectorand to which a circuit board is detachably connected through anexpansion connector, the circuit board including an internal circuitcomponent variably consuming power, comprising:power supply means,coupled to the power connector and the circuit board, for supplying anexternal power to said external equipment through the power connectorand supplying an internal power to said internal circuit componentthrough the expansion connector; means, coupled to said power supplymeans, for detecting whether an amount of the internal power suppliedfrom said power supply means exceeds a predetermined value; and means,coupled to said detecting means, for preventing the external power frombeing supplied to said external equipment while said detecting meansdetects that the amount of internal power supplied from said powersupply means exceeds the predetermined value, thereby enabling saidpower supply means to supply the internal power for a normal operationof said internal circuit component.
 11. An equipment according to claim10, further comprising means, coupled to said preventing means, forinforming a user of said external equipment that the external power isnot supplied to said external equipment while said preventing meansprevents the external power from being supplied to said externalequipment.
 12. An equipment according to claim 10, wherein saiddetecting means includes:current value measuring means, coupled to saidpower supply means, for measuring a current value of the external power;and comparing means for receiving a measurement value from said currentvalue measuring means and comparing the measurement value with apredetermined reference value.
 13. An equipment according to claim 10,wherein said external equipment comprises a portable computer and saidcircuit board comprises an expansion unit for expanding a function ofsaid portable computer.
 14. In an electronic equipment in which anexternal equipment is detachably connected through a power connector,and a power supply circuit supplies an external power to said externalequipment through the power connector and supplies an internal power toan internal circuit component variably consuming the internal power, amethod of ensuring a normal operation of the internal circuit component,comprising the steps of:measuring a current value of the internal powersupplied from said power supply circuit to said internal circuitcomponent; comparing the measured current value with a predeterminedreference value; and preventing the external power from being suppliedto said external equipment when the measured current value exceeds thepredetermined reference value.
 15. A method according to claim 14,further comprising the step of informing a user of said externalequipment that the external power is not supplied to said externalequipment while the external power is prevented from being supplied tosaid external equipment.
 16. In an electronic equipment in which anexternal equipment is detachably connected to a power supply circuitthrough a power connector and a circuit board, including an internalcircuit component which variably consumes power supplied to saidinternal circuit component, is detachably connected through an expansionconnector to said power supply circuit, said power supply circuitsupplying an external power to said external equipment through the powerconnector and supplying an internal power to said internal circuitcomponent through the expansion connector, a method of ensuring a normaloperation of the internal circuit component, comprising the stepsof:measuring a current value of the internal power supplied from saidpower supply circuit; comparing the measured current value with apredetermined reference value; and preventing the external power frombeing supplied to said external equipment through said power connectorwhile the amount of the measured current value exceeds the predeterminedreference value.
 17. A method according to claim 16, further comprisingthe step of informing a user of said external equipment that theexternal power is not supplied to said external equipment when theexternal power is prevented from being supplied to said externalequipment.
 18. An expansion unit for expanding a function of a portablecomputer removably connected to the expansion unit, comprising:anexpansion component having an internal circuit component; a power supplycircuit supplying a first power to the portable computer and a secondpower to the internal circuit component; a detector which detects thesecond power supplied from the power supply circuit; and a controllerwhich prevents supply of the first power to the portable computer whenthe detector detects that the second power exceeds a predeterminedvalue.
 19. An expansion unit according to claim 18, wherein thecontroller outputs an alarm signal for informing that the first power isnot supplied to the portable computer when the controller preventssupply of the first power to the portable computer.
 20. An expansionunit according to claim 19, further comprising a speaker driven inresponse to the alarm signal.